There have been known respective rear wheel suspensions for a motorcycle in which a rear cushion is laid at the upper portion of a vehicle body so as to extend in the back and forth direction of the vehicle body (see e.g. Japanese Patent Publication No. Hei 1-34830) and in which a rear cushion is disposed to extend in the up-and-down direction of the vehicle body (see e.g. Japanese Patent Laid-open No. 2004-352209).
In the rear wheel suspension of the motorcycle described in Japanese Patent Publication No. Hei 1-34830 mentioned above, the rear cushion is disposed horizontally in the back and forth direction. Therefore, the space occupied by a rear cushion mechanism can be reduced and the stroke of the rear cushion is ensured to enhance shock absorption. However, a link member is needed to make an acting direction of shock from a road surface horizontal in the back and forth direction. In addition, since the rear cushion is disposed at the upper portion of the vehicle body, there is a problem in that the gravity center of the vehicle should be lowered.
In the rear wheel suspension of the motorcycle in described Japanese Patent Laid-open No. 2004-352209 mentioned above, the rear cushion is disposed vertically with respect to the vehicle body. Therefore, there is a problem in that such arrangement provides limitation when the stroke of the rear cushion is intended to be increased.
There has also been known a swing arm attachment structure for a motorcycle widthwise gap defined between a body frame and the swing arm by axially moving an adjusting collar fitted to a support shaft (see Japanese Patent No. 2564078).
In the swing arm attachment structure for a motorcycle described in Japanese Patent No. 2564078, a single swing arm is only swingably supported by a body frame but a swing arm attachment structure of a parallel link structure having two arms are not taken into consideration at all.
For the single swing arm, it is only needed that it is merely possible to adjust the vehicle-widthwise gap defined between the body frame and the single swing arm. For the swing arm of the parallel link structure, however, it is needed that the vehicle- widthwise gap between the body frame and two arms can be adjusted while adjusting the vehicle-widthwise relative positions of the two arms. Taking into account the assembly performance of the swing arms, it is desirable that the gap can be adjusted from the lateral side of the vehicle body.